1. Field of the Invention
The present invention relates generally to implantable medical devices, and more particularly to an apparatus for imparting selected bends in an implantable tubular device, such as a cardiac stimulator lead or a catheter.
2. Description of the Related Art
Implantable tubular structures, such as catheters, cardiac stimulator leads, shunts, and others are presently used for a variety of diagnostic and therapeutic purposes. The particular shape indicated for a given implantable tubular structure is dictated in large part by the anticipated physiological structures that will be encountered by the structure. For example, an endocardial lead attached distally to the ventricular apex may have a relatively straight shape. However, other situations may call for a more particularly shaped implantable tubular structure. For example, cardiac stimulator leads intended for implantation in the right atrium or coronary sinus are advantageously provided with one or more pre-established permanent bends in the tubular structure to either facilitate entry of the tubular structure into an obliquely disposed passageway, such as the coronary sinus, or to enable the tubular structure to conform with and thereby engage the internal structure of the right atrium to anchor the tubular structure in a particular position.
Presently, some effort is made by medical device manufacturers to supply implantable tubular structures with preselected shapes intended to accommodate particularized physiological structures. These commercially available devices are often supplied in different lengths, and with a variety of different types of preestablished bends. The sizes and preestablished shapes of these conventional devices are typically based on some empirically determined norm for the size and shape of the average anatomical structure to be encountered by the implantable device. The disadvantage associated with using conventional off-the-shelf implantable tubular devices is that internal anatomy varies greatly among individual patients. For this reason, a cardiac stimulator lead that may fit one patient may not be suitable for another patient. For those patients whose internal anatomy differs significantly from the hypothetical norm, the use of an off-the-shelf implantable tubular device may represent a compromise that, while not necessarily life threatening, may nevertheless involve a less than optimal treatment regimen.
For example, a cardiac stimulator lead is normally implanted into the heart by passing a lead through the superior vena cava and into the right atrium. The pathway from the superior vena cava to the right atrium is relatively straight. However, the coronary sinus ostium is located approximately at a 90xc2x0 angle from that straight pathway. If the lead must be implanted in the coronary sinus, the lead must negotiate the 90xc2x0 turn to successfully enter the coronary sinus ostium. Examples are legion of other anatomical structures where significant changes in direction are associated with the implantation pathway.
Another conventional device incorporates a bellows joint for establishing a shape in a catheter. The capability of this system to customize an implantable tubular device is limited in several aspects. First, the types of shapes that may be imparted are normally limited to two dimensions. Second, the portion of the catheter that may be shaped is limited to the immediate vicinity of the bellows joint.
The present invention is directed to overcoming or reducing one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, an apparatus for establishing a preselected shape in an implantable tubular device is provided. The apparatus includes a sleeve composed of a heat-sensitive shape-memory material. The sleeve has an inside diameter of sufficient size such that the sleeve may be placed around the implantable tubular device at the preselected location. The sleeve may be heated above the glass transition temperature for the heat-sensitive shape-memory material, deformed to establish the preselected shape and cooled the below the glass transition temperature to harden the sleeve so that the preselected shape is retained.
In accordance with another aspect of the present invention, an apparatus for establishing a preselected shape in an implantable tubular device is provided. The apparatus includes a first sleeve having an inside diameter of sufficient size such that the first sleeve may be placed around the implantable tubular device at the preselected location. An elongated rib is coupled to the first sleeve. The elongated rib is plastically deformable so that when a bend is introduced into the first sleeve, the elongated rib retains the introduced bend.
In accordance with still another aspect of the present invention, a method of imparting a bend at a preselected location along the length of an implantable tubular device is provided. The method includes the steps of slipping a tubular sleeve over the implantable tubular device and positioning the sleeve at the preselected location. The sleeve is plastically deformed to impart the bend.
In accordance with another aspect of the present invention, an apparatus for establishing a preselected shape in an implantable tubular device is provided. The apparatus includes a sleeve that is composed of a polymeric material that hardens upon exposure to chemical, photo, or heat stimulation. The sleeve has an inside diameter of sufficient size such that the sleeve may be placed around the implantable tubular device. The sleeve may be deformed to establish the preselected shape and exposed to chemical, photo, or heat stimulation to harden the sleeve so that the preselected shape is retained.
In accordance with still another aspect of the present invention, a cardiac stimulator lead is provided. The cardiac stimulator lead includes a tubular lead body and a sleeve coupled to the exterior of the tubular lead body. The sleeve is composed of a polymeric material that hardens upon exposure to chemical, photo, or heat stimulation. The sleeve may be deformed to establish the preselected shape in the tubular lead body and exposed to chemical, photo, or heat stimulation to harden the sleeve so that the preselected-shape is retained.
In accordance with yet another aspect of the present invention, an apparatus for establishing a preselected shape in an implantable tubular device is provided. The apparatus includes a sleeve that is composed of a shape memory metal coated with a biocompatible polymeric material. The sleeve has an initial inside diameter of sufficient size such that the sleeve may be placed around the implantable tubular device. The sleeve may be heated and caused to decrease in diameter to engage the outer surface of the implantable tubular device, and deformed to establish the preselected shape.